This invention relates to a material embrittlement system, more particularly to a material embrittlement system for treatment of thermoset and thermoplastic materials by contacting the materials with "dry ice" transformed from a naturally occurring CO.sub.2 gas well.
A wide variety of industrial operations grind or chop materials for further processing. It is extremely difficult today, however, economically to reduce the size of many substances, including scrap materials, to the fineness necessary for further processing. Although, once reduced, many scrap materials, such as rubber, plastics, roofing, and other thermoset and thermoplastic materials, can be beneficially used in industrial applications either directly or indirectly by blending with virgin materials. Scrap rubber from tires, for example, are a high quality rubber source, but are very tough and require considerable energy to grind into a useful product. In addition, scrap materials are often difficult to handle during size reduction due to their tendency to become tacky and agglomerate when processed using normal milling, chopping or grinding techniques.
A variety of conventional methods are available for reducing the size of materials. For example, ambient grinding processes are commonly used, but are only capable of reducing the particle size of the material to approximately 50 mesh (U.S. Standard). This limitation is attributed to heat buildup in grinding which causes agglomeration of thermoset and thermoplastic particles. Alternatively, wet grinding processes are available which grind particles finer than conventional ambient processes. Wet grinding processes, however, generally require extra energy input to separate and to dry the particles. In addition, wet processes create air and water pollution concerns.
Moreover, cryogenic processes have been developed which achieve increased particle size reduction while using conventional ambient grinding techniques. Liquid nitrogen is often used in the cryogenic process to embrittle the material prior to grinding. This precooling eliminates heat buildup, and thus lessens the chance of particle agglomeration in the grinder. In this manner, size reduction down to 100 mesh and finer can be achieved. However, most cryogenic processes using liquid nitrogen are very expensive due to gas loss, high consumption of electrical energy, and extra equipment required to produce the liquid nitrogen. Cryogenic processes can also use "dry ice" (i.e., solid CO.sub.2) or compressed CO.sub.2 to embrittle the feed material prior to grinding. However, like liquid nitrogen, a great amount of energy is required to compress the CO.sub.2 gas into "dry ice". These additional costs tend to limit the use of cryogenic grinding to high value materials.
The present invention is directed accordingly to a system for the treatment of thermoset and thermoplastic materials to form an embrittled product at a heretofore unattainable low cost with minimal pollution control problems. The system comprises a naturally occurring CO.sub.2 gas well, a pressure-reduction conduit coupled to the CO.sub.2 gas well, pressure control valves for regulating the flow of the CO.sub.2 gas through the pressure-reduction conduit, a cryogenic chamber for transforming the CO.sub.2 gas flowing through the pressure-reduction conduit to dry ice snow, and a feed line for inserting the materials into the chamber for contact with the "dry ice" snow. The system is ideally suited to embrittle scrap materials for processing in a variety of conventional grinders for incorporation into new high quality products. However, the system can be used to embrittle various virgin materials as well. Additionally, the low manufacturing cost associated with the system when compared with conventional wet processing and other cryogenic processes will lead to greater customer acceptance of recycled materials. A greater consumption of recycled materials will be of special benefit to the environment.
The present invention is further directed to a process for treating thermoset and thermoplastic materials to form a substantially embrittled product. The process comprises extracting high pressure CO.sub.2 gas from naturally occurring CO.sub.2 well. The high pressure CO.sub.2 gas is fed into a pressure-reduction conduit. At least one pressure-control valve, positioned within the pressure-reduction conduit, is manipulated to allow predetermined portions of CO.sub.2 gas to flow through the pressure-reduction conduit at increasingly stepped-down pressures. Once the pressure of the CO.sub.2 gas has reached a controlled pressure conducive to forming "dry ice", the CO.sub.2 gas is released into a non-pressurized cryogenic cooling chamber. The CO.sub.2 gas is converted into a very cold "dry ice" snow as it enters the cryogenic cooling chamber. The material is contacted with the "dry ice" snow to form an embrittled product suitable for either grinding or for other process where embrittlement is desired.
Other objects and features of the present invention will become apparent as this description progresses.